Since electricity is an expensive utility, one step towards conservation is to design buildings that reduce demand of electricity purchased from the power grid. One way to reduce the amount of energy required to be purchased to power the building is to supplement or replace reliance on energy purchased from the power grid by using renewable sources of energy such as solar energy to power the building and devices within the building.
One example of using solar energy is the use of photovoltaic arrays on the outer surfaces of buildings and structures, such as the roofs and outer walls of the building or structure. Such photovoltaic arrays can be attached to the building and interconnected after the building is built, thus allowing a building to be retrofitted to use renewable energy. In general, a photovoltaic cell or photocell is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect.